1. Field
The present invention generally relates to a measurement system and method, and particularly to a measurement system and method for measuring a change in the refractive index of a lens.
2. Description of Related Art
Generally, optical lenses are manufactured by injection molding, which is advantageous for mass production at a low cost. During injection molding of the lenses, upper and lower molds are assembled to correspond to the desired contour of the lens, which is formed by injecting a molten material into a space between the molds.
However, internal force can be generated within a body of the lens due to defects on the molds or imprecision in manufacturing, with internal stress distributed where the internal force occurs. A change in the refractive index of the lens may correspondingly occur in the area where the internal stress is distributed.
Referring to FIG. 4, a conventional measurement system 20 for detecting a change in the refractive index of a lens experiencing internal stress includes a first polarizer 201, a second polarizer 202, and a light source 203 stacked in that order. The lens 30 to be measured is disposed between the first polarizer 201 and the second polarizer 202. In use, the light source 203 emits light through the second polarizer 202, the lens 30, and the first polarizer 201. An operator observes emitted light with the naked eye from an end away from the light source 203. Because the interference of light waves can be observed when the refractive index of the lens 30 changes, location of the internal stress in the lens can be detected accordingly. However, such measures cannot precisely detect the magnitude of the change in the refractive index.
What is needed, therefore, is a measurement system and method providing improved and reliable results.